Will it fold? Look in Power Query Online!

Query folding is a key capability in Power Query. In short, query folding is the process by which the Power Query mashup engine takes the steps defined in the Power Query editor and translates them into processing to be performed by the data source from which the query is extracting data.

The use of query folding can produce significant performance improvements. Consider a query that includes a grouping step. Without query folding, all of the detailed data required must be extracted from the data source, and the aggregation performed by the mashup engine. With query folding, the mashup engine can add a GROUP BY clause[1] to the data source query it generates, and lets the data source perform the costly operation – only the aggregated data leaves the data source.

Because of the performance benefit that query folding provides, experienced query authors are typically very careful to ensure that their queries take advantage of the capabilities of their data sources, and that they fold as many operations as possible. But for less experienced query authors, telling what steps will fold and which will not has not always been simple…

Until now.

This week the Power Query team announced the introduction of query folding indicators in Power Query Online. If you’re authoring a dataflow in Power BI or Power Apps, you will now see visual indicators to let you know which steps will fold, and which will not.

Each step will include an icon[2] that shows how that step will be handled. The announcement blog post goes into more details (because connectivity and data access are complicated topics, and because of the huge diversity in the data sources to which Power Query can connect) but the short version of the story is that life just got simpler for people who build dataflows.

After the last 12 months anything that makes my life simpler is a good thing.


[1] Or whatever the syntax is for the data source being used.

[2] Or is it a logo?

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